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Effects of soil compaction on the growth and mortality of planted dipterocarp seedlings in a logged-over tropical rainforest in Sarawak, Malaysia
Forest Ecology and Management 310 (2013) 770–776
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Effects of soil compaction on the growth and mortality of planted dipterocarp seedlings in a logged-over tropical rainforest in Sarawak, Malaysia Daisuke Hattori a,1, Tanaka Kenzo b,⇑, Kazuo Okamura Irino c, Joseph Jawa Kendawang d, Ikuo Ninomiya e, Katsutoshi Sakurai f a
United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan c Center for Cooperative Research and Development, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan d Sarawak Planted Forest, Wisma Sumber Alam, Jalan Stadium, Petra Jaya, 93660 Kuching, Sarawak, Malaysia e Faculty of Agriculture, Ehime University, Matsuyama, Ehime 790-8566, Japan f Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan b
a r t i c l e
i n f o
Article history: Received 27 June 2013 Received in revised form 11 September 2013 Accepted 12 September 2013 Available online 7 October 2013 Keywords: Borneo Enrichment planting Root elongation Skid trail Soil disturbance
a b s t r a c t Soil compaction is major determinant of plant growth and/or mortality. Tropical rainforests in Southeast Asia have been degraded by commercial logging, and the use of heavy equipment in these operations has increased soil compaction. We conducted enrichment planting 20 years after logging in a tropical forest in Borneo to evaluate the effects of soil compaction on the growth and mortality of planted dipterocarp seedlings over seven years. We planted the seedlings in sites that had been impacted to varying degrees, including a skid trail and undisturbed areas. We measured soil nutrients, moisture content, bulk density, penetration resistance, and light conditions. Seedling mortality, height, and shoot diameter were also determined 0, 12, 24, and 81 months after planting. Elongation rates of tap and lateral roots were measured 24 months after planting. We also excavated seedlings 81 months after planting, and compared heights, shoot diameters, tap root length, and lateral root length between compacted and undisturbed soils. Bulk density varied in the range of 0.98–1.61 g cm3 and correlated with soil penetration resistance. Surface soil (0–20 cm depth) in the compacted area had two to three times more resistance to penetration than did undisturbed soils. Surface soil penetration resistance significantly increased seedling mortality during the early planting period (0–12 months), but mortality in the later periods (12–24 and 24–81 months) did not relate to the soil penetration resistance. The lateral root growth rate in the early planting period (0–24 months) was also significantly inhibited by penetration resistance, but tap root growth was not. Penetration resistance did not reduce the seedling growth rate in the periods 0–12 and 12–24 months after planting, and higher soil moisture promoted seedling shoot diameter growth in the same time periods. Lateral root elongation did not differ between compacted and undisturbed forest soils 81 months after planting, but tap root elongation was inhibited in the compacted area at that time. Our results suggest that soil compaction negatively affect root elongation and initial seedling survival of planted dipterocarp trees even in 20 years after logging operation in Bornean tropical rainforest. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Soil compaction has major influences on growth and/or mortality rates of plants (Kozlowski, 1999). Although mild compaction of soil may benefit plant growth, the use of heavy machinery at tim⇑ Corresponding author. Address: Department of Plant Ecology, Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki 305-8687, Japan. Tel.: +81 29 873 3211; fax: +81 29 874 3797. E-mail address: [email protected] (T. Kenzo). 1 Present address: Tokushima Center for Climate Change Actions, 1-23, Higashiokinosu, Tokushima 770-0873, Japan. 0378-1127/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2013.09.023
ber harvesting sites and heavy foot traffic in recreational areas usually lead to inhibition of plant growth, yield, and survival (Alameda and Villar, 2009; Kozlowski, 1999). Tropical rainforests in Southeast Asia that have high value timber and rich biodiversity have been largely degraded by commercial logging operations (Hansen, 2005; Imai et al., 2012; Kenzo et al., 2009; Laurance, 2007). Modern heavy equipment, such as bulldozers and skidders, produces the most serious soil compaction (Fredericksen and Pariona, 2002; Pinard et al., 2000; Whitman et al., 1997) in comparison with other anthropogenic activities, such as shifting cultivation, forest fires, and trampling (Alegre
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and Cassel, 1996; Rab, 1996; Talbot et al., 2003). At the most severely compacted sites in dipterocarp forests in Malaysia, including skid trails and log landings, the soils are 2.0–4.5 times harder than at undisturbed locations (Jusoff, 1991; Mohd and Ang, 1991). Compaction generally negatively alters soil structure and hydrology (i) by increasing bulk density, soil strength, water runoff, and erosion, (ii) by breaking down soil aggregation, and (iii) by decreasing porosity, aeration, and infiltration capacity (Bruenig, 1996; Jusoff, 1992; Jusoff and Majid, 1986, 1987; Kozlowski, 1999; Van der Plas and Bruijnzeel, 1993). Highly compacted soils inhibit natural regeneration of late-successional tropical forest trees (Howlett and Davidson, 2003; Nabe-Nielsen et al., 2007; Pinard et al., 1996, 2000). Enrichment planting of logged-over sites with dipterocarp trees (Dipterocarpaceae), which are the predominant canopy species and important timber sources in Southeast Asian forests, is the primary method of accelerating regeneration and rehabilitation of degraded forests (Ådjers et al., 1995; Appanah and Weinland, 1996; Kenzo et al., 2011). However, severe soil compaction may reduce the effectiveness of enrichment planting by lowering the growth and survival rates of planted seedlings. Previous conventional logging operations using bulldozers usually compacted substantial proportion of forest floor such as 12–58% of forest floor was compacted in many dipterocarp forests (Cannon et al., 1994; Chai, 1975; Jusoff, 1991; Pinard and Putz, 1996). Such compaction lowers the natural recruitment and growth rates of dipterocarp seedlings in loggedover forests of Borneo (Nussbaum et al., 1995a; Pinard et al., 1996, 2000). Determination of the extent of soil compaction and its effects on planted seedlings is therefore crucial for the development of appropriate enrichment planting protocols and for tracking recovery processes in degraded tropical forests. However, there are still only limited long-term monitoring data on the performance of dipterocarp seedlings in enrichment planting sites located in compacted areas of logged-over dipterocarp forests (Nussbaum et al., 1995a). In this study, we conducted enrichment planting at a site 20 years after logging had ceased to determine the effects of soil compaction on the growth and mortality of planted dipterocarp seedlings over a seven-year observation period. The study site was located in Sarawak State, Borneo, Malaysia. Our premise was that because heavy soil compaction has strong effects on the first phase of wild plant establishment (Alameda and Villar, 2009), it would also negatively influence the growth and survival of early stage planted dipterocarp seedlings. To test this postulate we measured effects of compaction on soil moisture, mineral nutrients, light conditions, and seedling performance.
2. Materials and methods
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cal properties have been reported by Hattori et al. (2005). The original vegetation consisted of a mixed dipterocarp forest. The forest was selectively cut by conventional logging operation in the early 1980s. After abandonment, regenerated trees were mainly pioneer taxa, such as Macaranga, Artocarpus, and Ficus (Hattori et al., 2013; Kenzo et al., 2010). 2.2. Experimental plots and planted trees Experimental enrichment planting in degraded forest has been underway in the Niah Forest Reserve since February 2000 (Ninomiya et al., 1999). Fourteen study plots (10 10 m) including compacted soil plots were randomly established in the forest. We were not able to discern by field observation the degree of soil disturbance in each of these plots because, other than on large skid trails and at log landings, vegetation recovery was almost complete 20 years after logging. Seven species of dipterocarp seedlings were planted in the plots. All seedlings were raised from seed derived from a mass flowering event in 1998–1999. Collected seeds were inserted into black polyethylene bags (approximately 10 cm in diameter and 16 cm in depth) containing forest subsoil. Seedlings that emerged were grown in a nursery under shade netting (40% full sunlight) for one year. In 2000, 36 pot-grown seedlings were planted at 2-m intervals in each experimental plot (in total, 504 individuals). We transplanted seedlings to planting holes (approximately 12–14 cm diameter and 20 cm deep). All seedlings were dipterocarps of the following species: Dryobalanops beccarii, Parashorea macrophylla, Shorea macrophylla, S. ovata, S. parvifolia, S. seminis, and S. virescens. All seven species are late-successional canopy trees that usually grow 40–50 m tall. Although all species originally had distributed in the forest reserve, most seed source trees (e.g. diameter at breast height P30 cm) have been degraded by the logging. Parameters of ecological traits, such as the photosynthetic rate, drought tolerance, and nutrient demand, are closely similar between species under the shade conditions of planted forests (Hattori et al., 2009; Kenzo et al., 2007). After planting, we measured environmental factors, including soil hardness, moisture, nutrient content, and light conditions, in the plots. Mortality rate, heights, and diameters at the bases of the seedlings were monitored 0, 12, 24, and 81 months after planting. We carefully excavated a total of 70 seedlings (all species) from the plots and measured lateral and tap root lengths 24 months after planting. We also excavated seedlings 81 months after planting and compared heights, shoot diameters, and tap and lateral root lengths between compacted (bulk density >1.2 g cm3) and undisturbed experimental treatments (bulk density 61.2 g cm3). There were three species among the excavated seedlings (P. macrophylla, S. ovata, and S. virescens) and these were planted in compacted (n = 19) and undisturbed soils (n = 16).
2.1. Study site 2.3. Measurements of light conditions and soil penetration resistance The study was conducted in the Niah Forest Reserve in Sarawak State, Borneo, Malaysia (40–50 m elevation, 3°390 N, 113°420 E). This region is classified as part of the ‘‘humid tropics’’; it has an average annual air temperature of 27 °C and an annual rainfall of 2800 mm. The slope of the terrain was gentle to moderate, with a gradient of <25° (KTA Agriculture Consultancy, 1993). Soil parent materials were derived from sedimentary rocks of the Setap Shale Formation (Haile, 1962). This formation, deposited in the Northwest Borneo Geosyncline, is composed of a thick succession of shale with subordinate sandstone and a few lenses of limestone. The shale is typically clayey, moderately soft, and well-bedded. Baillie (1972) described soil in an area of the Niah Forest Reserve adjoining our study site as composed of moderately soft gray mudstones and shale. This soil is classified as Typic Kandihumults by the USDA soil classification system (Soil Survey Staff, 1999). Detailed soil chemi-
We measured relative light intensity (RLI) 130 cm above ground level at 30 points in each plot using an illumination meter (Konica Minolta Co., Tokyo, Digital Illumination Meter T-1H) on a cloudy day. Soil hardness was measured with a Hasegawa-type cone penetrometer (Daito Techno Green Co., Tokyo, H-60) from the soil surface to 60 cm depth, with eight replicates for each plot in a period with little precipitation (June and July 2000). A 2.0-kg weight was dropped onto the apparatus from a height of 50 cm (after removing the litter layer), and the number of strikes required to drive the penetrometer to 60 cm depth was used as a measure of soil hardness (Ishizuka et al., 1998, 2000; Sakurai et al., 1998). Soil penetration resistance was calculated by the following formula:
E¼MGHC
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where E is soil penetration resistance (J), M is the mass of the penetrometer (2.0 kg), G is gravitational acceleration (9.8 m s2), H is the vertical drop of the penetrometer weight (0.5 m), and C is the count of strikes for each depth. 2.4. Soil sampling Soil samples were randomly collected at depths of 0–5 cm from six points in each plot. In each sample, we determined pH, exchangeable calcium, magnesium, potassium, and aluminum, cation exchange capacity, total carbon and nitrogen, available phosphorus, and clay content. The samples were mixed to create a composite sample, and then air-dried and passed through a 2-mm mesh sieve. Using a metal core (100 ml), we took three samples at a depth of 0–10 cm in each plot for determinations of soil bulk density and moisture content. All samples were taken in the morning between 0800 and 1000 in a same day.
Table 1 Average soil and light conditions in all plots.
pH Exchangeable Ca (cmolc kg1) Exchangeable Mg (cmolc kg1) Exchangeable K (cmolc kg1) Exchangeable Al (cmolc kg1) Cation exchange capacity (cmolc kg1) Total carbon (g kg1) Total nitrogen (g kg1) Available phosphorus (mg kg1) Clay content (%) Soil water (%) Bulk density (g cm3) Soil penetration resistance at 0–10 cm (J cm1) Soil penetration resistance at 10–20 cm (J cm1) Relative light intensity (%)
Mean
SE
n
5.05 2.81 1.61 0.43 1.73 16.31 40.8 3.6 8.7 28.7 33.0 1.3 2.42 5.07 5.57
0.08 0.47 0.21 0.04 0.40 0.65 1.9 0.0 0.6 0.9 0.8 0.0 0.15 0.21 0.73
14 14 14 14 14 14 14 14 14 14 14 42 112 112 420
Ca, calcium; Mg, magnesium; K, potassium; Al, aluminum. Values are means and standard errors (SE).
2.5. Analysis of soil chemical and physical properties We measured soil pH in water (1:5 soil to solution ratio) using the glass electrode method. Total carbon and nitrogen content were determined with a NC Analyzer (Sumika Chemical Analysis Service, Co., Tokyo; Sumigraph model NC-80). Available phosphorus content was determined using the Bray II method (Bray and Kurtz, 1945). Exchangeable aluminum was extracted with 1.0 M potassium chloride, and the concentration was measured by the titration procedure. Amounts of exchangeable bases (calcium, magnesium, and potassium) and the cation exchange capacity were measured after successive extractions with 1.0 M ammonium acetate (pH 7.0) and 10% sodium chloride. The amount of ammonium replaced by sodium was determined using the steam distillation method. Exchangeable base concentrations were determined by atomic absorption spectrometry (Shimadzu, Co., Kyoto; AA610S). Clay content was determined by the pipette method. We used the ring method to measure soil moisture and bulk density (Black, 1965). 2.6. Data analysis We performed stepwise multiple regressions to explore environmental effects on seedling mortality, growth rate, and root elongation across all plots. We selected soil water content, exchangeable potassium, total nitrogen, available phosphorus, relative light intensity, and soil penetration resistance at depths of 0–10 cm and 10–20 cm as explanatory variables in the regression model. We used analysis of variance (ANOVA) to test the significance of different responses in seedling height, shoot diameter, and tap and lateral root lengths between two categories of soil compaction (compacted and undisturbed) 81 months after planting. All analyses were performed with SPSS Ver. 11.5 software (IBM, Armonk, NY, USA). 3. Results 3.1. Soil and light conditions Soils in the study plots were relatively fertile as indicated by high cation exchange capacity, organic matter, and exchangeable bases (Table 1). Bulk density varied in the range of 0.98– 1.61 g cm3 and differed between experimental treatments (data not shown). Bulk density strongly correlated with soil penetration resistance (r = 0.75, p < 0.01). Plots with highly compacted areas had higher penetration resistances through all soil depths (0–60 cm; Fig. 1a) compared to undisturbed plots (Fig. 1b). Surface
soil (0–20 cm) in compacted plots was two to three times more resistant than undisturbed soil. More hard soils appeared in relatively deep soil layers (e.g., 35–60 cm depth) in the highly compacted plots (Fig. 1a). Relative light intensity was 5.6%, and there was little variation between experimental treatments (Table 1). Soil chemical properties, clay contents, and light conditions were not significantly different among plots (p > 0.05, ANOVA, data not shown). 3.2. Mortality and growth rates of planted seedlings Seedling mortalities across all plots were in the range of 2.8–69.4% in the first year of the experiment (0–12 months), 0.0– 54.5% in the second year (12–24 months), and 0.0–60.9% in the final period (24–81 months). The range of relative growth rates for seedling height (RGRh) across all plots also varied over time: 0.07–0.54 cm cm1 yr1 during the first year, 0.09–0.32 cm cm1 yr1 in the second year, and 0.00–0.29 cm cm1 yr1 in the final period (24–81 months). Similarly, there was temporal variation in the relative growth rates of seedling shoot diameters (RGRd): 0.02–0.79 mm mm1 yr1 in the first year, 0.04–0.16 mm mm1 yr1 in the second year, and 0.05–0.27 mm mm1 yr1 in the final period (24–81 months). Lateral root growth rates were lower in compacted soils than in undisturbed soil during the first two years (0–24 months, Fig. 2). Seedling growth rates during the early planting stage (0–12 and 12–24 months after planting) did not differ significantly among the seven tree species (ANOVA with Bonferroni correction). However, Parashorea macrophylla grew more slowly that the other species during the late period (24–81 months after planting, data not shown). 3.3. Effects of environmental conditions on seedling performances Soil penetration resistance (10–20 cm depth) was positively correlated with seedling mortality during the early planting period (0–12 months) (multiple regression analysis, p < 0.01, standardized regression coefficient = 0.679, Table 2). However, mortalities in the later periods (12–24 and 24–84 months) were not correlated with soil penetration resistance (Table 2). The lateral root growth rate during the first and second years was inhibited by high soil penetration resistance (p < 0.01, standardized regression coefficient = 0.673), but tap root growth was not related to soil hardness (Table 2). Elevated soil moisture was related to the increased seedling RGR of shoot diameter in the first and second years, but soil moisture content was not correlated with the RGR
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(a) Compacted
Soil depth (cm)
0-5
0-5
5-10
5-10
10-15
10-15
15-20
15-20
20-25
20-25
25-30
25-30
30-35
30-35
35-40
35-40
40-45
40-45
45-50
45-50
50-55
50-55
55-60
55-60 0.0
10.0
20.0
30.0
(b) undisturbed
0.0
Soil penetration resistance (J
10.0
20.0
30.0
cm-1)
Fig. 1. Soil penetration resistance at a depth of 0–60 cm between (a) compacted soil and (b) undisturbed soil. Bars indicate standard error.
(a) Compacted soil
of height. Relative light intensity (RLI) was not related to any of the measures of seedling growth and mortality across all time periods. Soil nutrients, such as nitrogen, phosphorus, and potassium contents, were also not correlated with seedling mortalities or growth rates (Table 2). Tap root length was significantly shorter in compacted soil (40.6 cm) than in undisturbed soil 81 months after planting (61.5 cm, Table 3). However, seedling height, shoot diameter, and lateral root length were not significantly different between compacted and undisturbed soils.
(b) Undisturbed soil
4. Discussion 4.1. Soil disturbance 20 years after logging operations had ended 10cm
10cm
Fig. 2. Examples of excavated root systems in (a) compacted soil and (b) undisturbed soil 24 months after planting. The species excavated was Dryobalanops beccarii. Arrows indicate the soil surface.
More than 20 years after logging operations had ceased, logging disturbance still had an effect on surface soil compaction in the dipterocarp stand that we studied. Effects of compaction were large at soil depths of 0–20 cm in the disturbed area we examined,
Table 2 Stepwise multiple regression analysis of the effects of explanatory environmental factors on seedling relative height, shoot diameter, root growth rates, and mortality. [Soil total nitrogen (N), available phosphorus (P), exchangeable potassium (K), relative light intensity (RLI), soil water, and soil penetration resistance at the depth of 0–10 cm and 10–20 cm]. Dependent variable
Lateral root growth rate during 0–24 months (cm year1) Tap root growth rate during 0–24 months (cm year1) RGRh during 0–12 months (cm cm1 year1) RGRh during 12–24 months (cm cm1 year1) RGRh during 24–81 months (cm cm1 year1) RGRd during 0–12 months (mm mm1 year1) RGRd during 12–24 months (mm mm1 year1) RGRd during 24–81 months (mm mm1 year1) Mortality during 0–12 months (%) Mortality during 12–24 months (%) Mortality during 24–81 months (%)
Adjusted R2
Explanatory variables N
P
K
RLI
Soil water
Penetration resistance (0–10 cm)
Penetration resistance (10–20 cm)
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – 0.663** 0.666** – – – –
– – – – – – – – – – –
0.673** – – – – – – – 0.679** – –
0.407 – – – – 0.393 0.396 – 0.416 – –
RGRh, relative growth rate of seedlings height. RGRd, relative growth rate of seedlings diameter. Standardized regression coefficients, significance levels, and adjusted R2 values are given. n = 14. –, Data not selected by the analysis. ** p < 0.01. Unsuitable explanatory variables were excluded by the stepwise procedure (Fin = 0.05 > Fout = 0.1)
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Table 3 Comparison of soil penetration resistance, seedling height, shoot diameter, lateral root length and tap root length, between compacted and undisturbed soil 81 months after planting. Compacted soil
Soil penetration resistance at 0–20 cm (J cm1) Soil penetration resistance at 20–60 cm (J cm1) Height (cm) Diameter (mm) Lateral root length (cm) Tap root length (cm)
Undisturbed soil
Mean
SE
n
Mean
SE
n
6.80 14.52 227.3 21.5 36.0 40.6
0.37 1.00 24.1 1.3 3.2 4.9
19 19 19 19 19 19
3.24 5.21 233.1 22.3 41.3 61.5
0.20 0.38 20.3 1.6 8.7 4.9
16 16 16 16 16 16
** **
ns ns ns **
Values are means and standard errors (SE). ** p < 0.01; analysis of variance (ANOVA). ‘ns’ means not significantly differences.
and soil hardness increased with depth (Fig. 1). We compared levels of surface soil compaction with those in other logged tropical forests using soil bulk density as a measure; this parameter was significantly positively related to soil penetration resistance at our site. Bulk density is usually higher on log landings and skid trails than in undisturbed forest soils (Nussbaum and Ang, 1996). Bulk densities in uncompacted plots at our site (0.98–1.20 g cm3) were within the range of those in other undisturbed dipterocarp forest soils (0.98–1.27 g cm3; Jusoff and Majid, 1986, 1987; Pinard et al., 1996; Van der Plas and Bruijnzeel, 1993). The highest bulk density in our study area was 1.61 g cm3, a value at the upper end of the range reported by other studies of harvesting effects in tropical forests, including log landings and skid trails in logged-over dipterocarp forests (1.00–1.66 g cm3, Nussbaum and Ang, 1996; Nussbaum et al., 1995b; Van der Plas and Bruijnzeel, 1993). Our highest value was comparable to those for forest soils immediately after logging, e.g., 1.49 g cm3 in peninsular Malaysia (Jusoff and Majid, 1987) and 1.44 g cm3 in Sabah, Malaysia (Nussbaum et al., 1995a). The high bulk densities we measured indicated that soil compaction had not recovered naturally over the 20 years since logging had ceased. This protracted period of compaction is consistent with those in other forest biomes, such as temperate forests in which compaction may be elevated more than 40 years after disturbance (Vora, 1988). Although soil compaction was long-lasting, we did not find clear relationships between soil penetration resistance and nutrient contents, e.g., total nitrogen and phosphorus. However, several studies reported decreased nutrient content in soils disturbed by logging, particularly in sites immediately after logging and/or several years after disturbance (Kozlowski, 1999; Nussbaum et al., 1995b). Differences between our study and those at other sites may have resulted from litter accumulation in the Niah Forest Reserve. Leaf litters from regenerated secondary forest trees are usually nutrient-rich (Kenzo et al., 2010). Regenerated trees, such as Macaranga gigantea and M. hosei, reached almost 20 m in height and their crowns covered the disturbed areas, including the skid trail, where we found relatively thick litters in the wheel tracks. There are reports that pioneer species such as Macaranga spp. are able to regenerate on compacted soil and their growth is not retarded except at log landings. In contrast, the establishment and growth of late-successional tree species, especially dipterocarps, are significantly suppressed under compacted soil conditions (Nabe-Nielsen et al., 2007; Nussbaum et al., 1995a; Pinard et al., 2000). In addition, erosion and mineral nutrient loss through surface water runoff after logging disturbance were less severe on the relatively gentle slope in our study plots than in other lowland tropical forests in Sarawak (e.g., Ishizuka et al., 2000). 4.2. Effects of soil compaction on planted seedlings Higher surface soil compaction (at 10–20 cm depth) inhibited lateral root growth and accelerated seedling mortality in the early
stages (0–24 months after planting), but did not affect mortality in the later stages or the seedling shoot growth rate across the whole study period (Table 2). The soil depths (10–20 cm) in which there were effects of compaction on mortality and lateral root elongation may relate to the planting-hole depth (20 cm) we used. During the early planting period, seedlings on compacted soil may have suffered from drought stress caused by limited water absorption by inhibited lateral roots, which were usually not able to grow out of the planting holes, even two years after planting (Fig. 2). Furthermore, increased bulk density usually reduces the water-holding capacity of compacted soil (Chauvel et al., 1991; Jusoff, 1991; Nussbaum et al., 1995a). Thus, drought in the early period after planting likely affected seedling mortality negatively. We found many dead seedlings with wilted leaves in a severely compacted area during a period of approximately two weeks without rain in the initial planting period (three months after planting, T. Kenzo, personal observation). Rubiah and Kamis (2003) examined drought responses of dipterocarp seedlings (Hopea odorata) to soil compaction treatments, demonstrating that high bulk density increases the sensitivity of seedlings to drought stress and leads to a reduction of seedling photosynthesis and stomatal conductance three months after planting in a nursery. Rubiah and Kamis (2003) also reported a reduction in drought sensitivity 12 months after planting due to the elongation of new roots. The increased shoot diameter growth rate under higher soil water conditions in our experiment also highlights the importance of water for seedlings during the early planting stages (Table 2). All of these data for early seedling growth stages were consistent with the reduced effects of soil compaction on mortality and height and diameter growth in the later period, 81 months after planting (Tables 2 and 3). In older seedlings, lateral root elongation did not differ between compacted and undisturbed soil, although tap root elongation was inhibited in the compacted area (Table 2). The tap roots were unable to penetrate beyond more than 40 cm depth in compacted soil, which likely relates to the very hard soils that we detected in the 30–45 cm depth range, where hardness was more than double that of surface soil (Fig. 1). 4.3. Amelioration of soil compaction in enrichment planting Development of an appropriate enrichment planting methodology for dipterocarp seedlings under compacted soil conditions is needed to reduce seedling mortality during the early planting stage and enhance the seedling growth rate in later stages. Nussbaum et al. (1995a) tested the effects of five treatment combinations (compacted soil with fertilizer, compacted soil with mulching, dug soil, dug soil with fertilizer, and replacement of top soil) on the growth of two species of dipterocarp seedlings (Dryobalanops lanceolata and Shorea leprosula), and demonstrated that fertilization was the most effective treatment for improved growth. Vincent and Davies (2003) reported the same fertilization effect for Dryobalanops aromatica and Shorea parvifolia. Many earlier experiments had
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monitoring periods of only 1–2 years, but longer term observations are required to confirm the effects of fertilizer on dipterocarp seedling growth because negative effects of chemical fertilization, such as decreased growth and spindly morphology probably become apparent after fertilizer treatment has ended (Irino et al., 2004, 2005). Removal of competing non-timber trees also enhances dipterocarp seedling growth after the late planting period (Kuusipalo et al., 1996; Pariona et al., 2003). Future investigations of appropriate procedures for soil compaction amelioration at enrichment planting sites in logged-over dipterocarp forests should be more protracted and extend beyond the seedling stage. 4.4. Conclusions Soil compaction measured by high soil bulk density and penetration resistance was still apparent more than 20 years after a dipterocarp forest had been logged-over. During the early planting period, inhibition of lateral root elongation in the compacted area increased the mortality rates of dipterocarp seedlings. However, soil compaction did not affect the mortality, growth, and lateral root elongation after the late planting period (81 months after planting). Successful enrichment planting of dipterocarp trees in compacted soils requires proper treatment to reduce seedlings mortality in the early planting period. Acknowledgements We thank Sarawak Forest Department and Sarawak Forest Corporation for assistance in our study. This work was partly supported by a Grant-in-Aid for Scientific Research (09NP0901, 13575038, and 17405031), the Nissay Foundation, and the Sasakawa Scientific Research Grant from The Japan Science Society (15-411). References Ådjers, G., Hadengganan, S., Kuusipalo, J., Nuryanto, K., Vesa, L., 1995. Enrichment planting of dipterocarps in logged-over forests: effect of width, direction and maintenance method of planting line on selected Shorea species. For. Ecol. Manage. 73, 271–277. Alameda, D., Villar, R., 2009. Moderate soil compaction; implications on growth and architecture in seedlings of 17 woody plant species. Soil Tillage Res. 103, 325– 331. Alegre, J.C., Cassel, D.K., 1996. Dynamics of soil physical properties under alternative systems to slash-and-burn. Agric. Ecosyst. Environ. 58, 39–48. Appanah, S., Weinland, G., 1996. Experience with planting dipterocarps in peninsular Malaysia. In: Schulte, A., Schöne, D. (Eds.), Dipterocarp Forest Ecosystems: Towards Sustainable Management. World Scientific, Singapore, pp. 411–445. Baillie, I.C., 1972. Report on a Detailed Examination of Soils of Silvicultural Research Plot 53, Niah Forest Reserve, Forest Department Sarawak, Kuching. Black, C.A., 1965. Method of Soil Analysis, Part I. American Society of Agronomy, Madison, Wisconsin. Bray, R.H., Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils. Soil Sci. 59, 39–45. Bruenig, E.F., 1996. Conservation and Management of Tropical Rainforests: An Integrated Approach to Sustainability. CAB International, Wallingford. Cannon, C.H., Peart, D.R., Leighton, M., Kartawinata, K., 1994. The structure of lowland rainforest after selective logging in west Kalimantan, Indonesia. For. Ecol. Manage. 67, 49–68. Chai, D.N.P., 1975. Enrichment planting in Sabah. Malays. For. 38, 271–277. Chauvel, A., Grimaldi, M., Tessier, D., 1991. Changes in soil pore-space distribution following deforestation and revegetation: an example from the Central Amazon Basin, Brazil. For. Ecol. Manage. 38, 259–271. Fredericksen, T.S., Pariona, W., 2002. Effect of skidder disturbance on commercial tree regeneration in logging gaps in a Bolivian tropical forest. For. Ecol. Manage. 171, 223–230. Haile, N.S., 1962. The geology and mineral resources of Suai-Baram Area, North Sarawak. Brit. Borneo Geol. Mem. 13, 176. Hansen, T.S., 2005. Spatio-temporal aspects of land use and land cover changes in the Niah catchment, Sarawak, Malaysia. Singapore J. Trop. Geo. 26, 170–190. Hattori, D., Sabang, J., Tanaka, S., Kendawang, J.J., Ninomiya, I., Sakurai, K., 2005. Soil characteristics under three vegetation types associated with shifting cultivation in a mixed dipterocarp forest in Sarawak, Malaysia. Soil Sci. Plant Nutr. 51, 231– 241.
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Effects of soil compaction on the growth and mortality of planted dipterocarp seedlings in a logged-over tropical rainforest in Sarawak, Malaysia Daisuke Hattori a,1, Tanaka Kenzo b,⇑, Kazuo Okamura Irino c, Joseph Jawa Kendawang d, Ikuo Ninomiya e, Katsutoshi Sakurai f a
United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan c Center for Cooperative Research and Development, Ehime University, Bunkyo-cho 3, Matsuyama 790-8577, Japan d Sarawak Planted Forest, Wisma Sumber Alam, Jalan Stadium, Petra Jaya, 93660 Kuching, Sarawak, Malaysia e Faculty of Agriculture, Ehime University, Matsuyama, Ehime 790-8566, Japan f Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan b
a r t i c l e
i n f o
Article history: Received 27 June 2013 Received in revised form 11 September 2013 Accepted 12 September 2013 Available online 7 October 2013 Keywords: Borneo Enrichment planting Root elongation Skid trail Soil disturbance
a b s t r a c t Soil compaction is major determinant of plant growth and/or mortality. Tropical rainforests in Southeast Asia have been degraded by commercial logging, and the use of heavy equipment in these operations has increased soil compaction. We conducted enrichment planting 20 years after logging in a tropical forest in Borneo to evaluate the effects of soil compaction on the growth and mortality of planted dipterocarp seedlings over seven years. We planted the seedlings in sites that had been impacted to varying degrees, including a skid trail and undisturbed areas. We measured soil nutrients, moisture content, bulk density, penetration resistance, and light conditions. Seedling mortality, height, and shoot diameter were also determined 0, 12, 24, and 81 months after planting. Elongation rates of tap and lateral roots were measured 24 months after planting. We also excavated seedlings 81 months after planting, and compared heights, shoot diameters, tap root length, and lateral root length between compacted and undisturbed soils. Bulk density varied in the range of 0.98–1.61 g cm3 and correlated with soil penetration resistance. Surface soil (0–20 cm depth) in the compacted area had two to three times more resistance to penetration than did undisturbed soils. Surface soil penetration resistance significantly increased seedling mortality during the early planting period (0–12 months), but mortality in the later periods (12–24 and 24–81 months) did not relate to the soil penetration resistance. The lateral root growth rate in the early planting period (0–24 months) was also significantly inhibited by penetration resistance, but tap root growth was not. Penetration resistance did not reduce the seedling growth rate in the periods 0–12 and 12–24 months after planting, and higher soil moisture promoted seedling shoot diameter growth in the same time periods. Lateral root elongation did not differ between compacted and undisturbed forest soils 81 months after planting, but tap root elongation was inhibited in the compacted area at that time. Our results suggest that soil compaction negatively affect root elongation and initial seedling survival of planted dipterocarp trees even in 20 years after logging operation in Bornean tropical rainforest. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Soil compaction has major influences on growth and/or mortality rates of plants (Kozlowski, 1999). Although mild compaction of soil may benefit plant growth, the use of heavy machinery at tim⇑ Corresponding author. Address: Department of Plant Ecology, Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki 305-8687, Japan. Tel.: +81 29 873 3211; fax: +81 29 874 3797. E-mail address: [email protected] (T. Kenzo). 1 Present address: Tokushima Center for Climate Change Actions, 1-23, Higashiokinosu, Tokushima 770-0873, Japan. 0378-1127/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2013.09.023
ber harvesting sites and heavy foot traffic in recreational areas usually lead to inhibition of plant growth, yield, and survival (Alameda and Villar, 2009; Kozlowski, 1999). Tropical rainforests in Southeast Asia that have high value timber and rich biodiversity have been largely degraded by commercial logging operations (Hansen, 2005; Imai et al., 2012; Kenzo et al., 2009; Laurance, 2007). Modern heavy equipment, such as bulldozers and skidders, produces the most serious soil compaction (Fredericksen and Pariona, 2002; Pinard et al., 2000; Whitman et al., 1997) in comparison with other anthropogenic activities, such as shifting cultivation, forest fires, and trampling (Alegre
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and Cassel, 1996; Rab, 1996; Talbot et al., 2003). At the most severely compacted sites in dipterocarp forests in Malaysia, including skid trails and log landings, the soils are 2.0–4.5 times harder than at undisturbed locations (Jusoff, 1991; Mohd and Ang, 1991). Compaction generally negatively alters soil structure and hydrology (i) by increasing bulk density, soil strength, water runoff, and erosion, (ii) by breaking down soil aggregation, and (iii) by decreasing porosity, aeration, and infiltration capacity (Bruenig, 1996; Jusoff, 1992; Jusoff and Majid, 1986, 1987; Kozlowski, 1999; Van der Plas and Bruijnzeel, 1993). Highly compacted soils inhibit natural regeneration of late-successional tropical forest trees (Howlett and Davidson, 2003; Nabe-Nielsen et al., 2007; Pinard et al., 1996, 2000). Enrichment planting of logged-over sites with dipterocarp trees (Dipterocarpaceae), which are the predominant canopy species and important timber sources in Southeast Asian forests, is the primary method of accelerating regeneration and rehabilitation of degraded forests (Ådjers et al., 1995; Appanah and Weinland, 1996; Kenzo et al., 2011). However, severe soil compaction may reduce the effectiveness of enrichment planting by lowering the growth and survival rates of planted seedlings. Previous conventional logging operations using bulldozers usually compacted substantial proportion of forest floor such as 12–58% of forest floor was compacted in many dipterocarp forests (Cannon et al., 1994; Chai, 1975; Jusoff, 1991; Pinard and Putz, 1996). Such compaction lowers the natural recruitment and growth rates of dipterocarp seedlings in loggedover forests of Borneo (Nussbaum et al., 1995a; Pinard et al., 1996, 2000). Determination of the extent of soil compaction and its effects on planted seedlings is therefore crucial for the development of appropriate enrichment planting protocols and for tracking recovery processes in degraded tropical forests. However, there are still only limited long-term monitoring data on the performance of dipterocarp seedlings in enrichment planting sites located in compacted areas of logged-over dipterocarp forests (Nussbaum et al., 1995a). In this study, we conducted enrichment planting at a site 20 years after logging had ceased to determine the effects of soil compaction on the growth and mortality of planted dipterocarp seedlings over a seven-year observation period. The study site was located in Sarawak State, Borneo, Malaysia. Our premise was that because heavy soil compaction has strong effects on the first phase of wild plant establishment (Alameda and Villar, 2009), it would also negatively influence the growth and survival of early stage planted dipterocarp seedlings. To test this postulate we measured effects of compaction on soil moisture, mineral nutrients, light conditions, and seedling performance.
2. Materials and methods
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cal properties have been reported by Hattori et al. (2005). The original vegetation consisted of a mixed dipterocarp forest. The forest was selectively cut by conventional logging operation in the early 1980s. After abandonment, regenerated trees were mainly pioneer taxa, such as Macaranga, Artocarpus, and Ficus (Hattori et al., 2013; Kenzo et al., 2010). 2.2. Experimental plots and planted trees Experimental enrichment planting in degraded forest has been underway in the Niah Forest Reserve since February 2000 (Ninomiya et al., 1999). Fourteen study plots (10 10 m) including compacted soil plots were randomly established in the forest. We were not able to discern by field observation the degree of soil disturbance in each of these plots because, other than on large skid trails and at log landings, vegetation recovery was almost complete 20 years after logging. Seven species of dipterocarp seedlings were planted in the plots. All seedlings were raised from seed derived from a mass flowering event in 1998–1999. Collected seeds were inserted into black polyethylene bags (approximately 10 cm in diameter and 16 cm in depth) containing forest subsoil. Seedlings that emerged were grown in a nursery under shade netting (40% full sunlight) for one year. In 2000, 36 pot-grown seedlings were planted at 2-m intervals in each experimental plot (in total, 504 individuals). We transplanted seedlings to planting holes (approximately 12–14 cm diameter and 20 cm deep). All seedlings were dipterocarps of the following species: Dryobalanops beccarii, Parashorea macrophylla, Shorea macrophylla, S. ovata, S. parvifolia, S. seminis, and S. virescens. All seven species are late-successional canopy trees that usually grow 40–50 m tall. Although all species originally had distributed in the forest reserve, most seed source trees (e.g. diameter at breast height P30 cm) have been degraded by the logging. Parameters of ecological traits, such as the photosynthetic rate, drought tolerance, and nutrient demand, are closely similar between species under the shade conditions of planted forests (Hattori et al., 2009; Kenzo et al., 2007). After planting, we measured environmental factors, including soil hardness, moisture, nutrient content, and light conditions, in the plots. Mortality rate, heights, and diameters at the bases of the seedlings were monitored 0, 12, 24, and 81 months after planting. We carefully excavated a total of 70 seedlings (all species) from the plots and measured lateral and tap root lengths 24 months after planting. We also excavated seedlings 81 months after planting and compared heights, shoot diameters, and tap and lateral root lengths between compacted (bulk density >1.2 g cm3) and undisturbed experimental treatments (bulk density 61.2 g cm3). There were three species among the excavated seedlings (P. macrophylla, S. ovata, and S. virescens) and these were planted in compacted (n = 19) and undisturbed soils (n = 16).
2.1. Study site 2.3. Measurements of light conditions and soil penetration resistance The study was conducted in the Niah Forest Reserve in Sarawak State, Borneo, Malaysia (40–50 m elevation, 3°390 N, 113°420 E). This region is classified as part of the ‘‘humid tropics’’; it has an average annual air temperature of 27 °C and an annual rainfall of 2800 mm. The slope of the terrain was gentle to moderate, with a gradient of <25° (KTA Agriculture Consultancy, 1993). Soil parent materials were derived from sedimentary rocks of the Setap Shale Formation (Haile, 1962). This formation, deposited in the Northwest Borneo Geosyncline, is composed of a thick succession of shale with subordinate sandstone and a few lenses of limestone. The shale is typically clayey, moderately soft, and well-bedded. Baillie (1972) described soil in an area of the Niah Forest Reserve adjoining our study site as composed of moderately soft gray mudstones and shale. This soil is classified as Typic Kandihumults by the USDA soil classification system (Soil Survey Staff, 1999). Detailed soil chemi-
We measured relative light intensity (RLI) 130 cm above ground level at 30 points in each plot using an illumination meter (Konica Minolta Co., Tokyo, Digital Illumination Meter T-1H) on a cloudy day. Soil hardness was measured with a Hasegawa-type cone penetrometer (Daito Techno Green Co., Tokyo, H-60) from the soil surface to 60 cm depth, with eight replicates for each plot in a period with little precipitation (June and July 2000). A 2.0-kg weight was dropped onto the apparatus from a height of 50 cm (after removing the litter layer), and the number of strikes required to drive the penetrometer to 60 cm depth was used as a measure of soil hardness (Ishizuka et al., 1998, 2000; Sakurai et al., 1998). Soil penetration resistance was calculated by the following formula:
E¼MGHC
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where E is soil penetration resistance (J), M is the mass of the penetrometer (2.0 kg), G is gravitational acceleration (9.8 m s2), H is the vertical drop of the penetrometer weight (0.5 m), and C is the count of strikes for each depth. 2.4. Soil sampling Soil samples were randomly collected at depths of 0–5 cm from six points in each plot. In each sample, we determined pH, exchangeable calcium, magnesium, potassium, and aluminum, cation exchange capacity, total carbon and nitrogen, available phosphorus, and clay content. The samples were mixed to create a composite sample, and then air-dried and passed through a 2-mm mesh sieve. Using a metal core (100 ml), we took three samples at a depth of 0–10 cm in each plot for determinations of soil bulk density and moisture content. All samples were taken in the morning between 0800 and 1000 in a same day.
Table 1 Average soil and light conditions in all plots.
pH Exchangeable Ca (cmolc kg1) Exchangeable Mg (cmolc kg1) Exchangeable K (cmolc kg1) Exchangeable Al (cmolc kg1) Cation exchange capacity (cmolc kg1) Total carbon (g kg1) Total nitrogen (g kg1) Available phosphorus (mg kg1) Clay content (%) Soil water (%) Bulk density (g cm3) Soil penetration resistance at 0–10 cm (J cm1) Soil penetration resistance at 10–20 cm (J cm1) Relative light intensity (%)
Mean
SE
n
5.05 2.81 1.61 0.43 1.73 16.31 40.8 3.6 8.7 28.7 33.0 1.3 2.42 5.07 5.57
0.08 0.47 0.21 0.04 0.40 0.65 1.9 0.0 0.6 0.9 0.8 0.0 0.15 0.21 0.73
14 14 14 14 14 14 14 14 14 14 14 42 112 112 420
Ca, calcium; Mg, magnesium; K, potassium; Al, aluminum. Values are means and standard errors (SE).
2.5. Analysis of soil chemical and physical properties We measured soil pH in water (1:5 soil to solution ratio) using the glass electrode method. Total carbon and nitrogen content were determined with a NC Analyzer (Sumika Chemical Analysis Service, Co., Tokyo; Sumigraph model NC-80). Available phosphorus content was determined using the Bray II method (Bray and Kurtz, 1945). Exchangeable aluminum was extracted with 1.0 M potassium chloride, and the concentration was measured by the titration procedure. Amounts of exchangeable bases (calcium, magnesium, and potassium) and the cation exchange capacity were measured after successive extractions with 1.0 M ammonium acetate (pH 7.0) and 10% sodium chloride. The amount of ammonium replaced by sodium was determined using the steam distillation method. Exchangeable base concentrations were determined by atomic absorption spectrometry (Shimadzu, Co., Kyoto; AA610S). Clay content was determined by the pipette method. We used the ring method to measure soil moisture and bulk density (Black, 1965). 2.6. Data analysis We performed stepwise multiple regressions to explore environmental effects on seedling mortality, growth rate, and root elongation across all plots. We selected soil water content, exchangeable potassium, total nitrogen, available phosphorus, relative light intensity, and soil penetration resistance at depths of 0–10 cm and 10–20 cm as explanatory variables in the regression model. We used analysis of variance (ANOVA) to test the significance of different responses in seedling height, shoot diameter, and tap and lateral root lengths between two categories of soil compaction (compacted and undisturbed) 81 months after planting. All analyses were performed with SPSS Ver. 11.5 software (IBM, Armonk, NY, USA). 3. Results 3.1. Soil and light conditions Soils in the study plots were relatively fertile as indicated by high cation exchange capacity, organic matter, and exchangeable bases (Table 1). Bulk density varied in the range of 0.98– 1.61 g cm3 and differed between experimental treatments (data not shown). Bulk density strongly correlated with soil penetration resistance (r = 0.75, p < 0.01). Plots with highly compacted areas had higher penetration resistances through all soil depths (0–60 cm; Fig. 1a) compared to undisturbed plots (Fig. 1b). Surface
soil (0–20 cm) in compacted plots was two to three times more resistant than undisturbed soil. More hard soils appeared in relatively deep soil layers (e.g., 35–60 cm depth) in the highly compacted plots (Fig. 1a). Relative light intensity was 5.6%, and there was little variation between experimental treatments (Table 1). Soil chemical properties, clay contents, and light conditions were not significantly different among plots (p > 0.05, ANOVA, data not shown). 3.2. Mortality and growth rates of planted seedlings Seedling mortalities across all plots were in the range of 2.8–69.4% in the first year of the experiment (0–12 months), 0.0– 54.5% in the second year (12–24 months), and 0.0–60.9% in the final period (24–81 months). The range of relative growth rates for seedling height (RGRh) across all plots also varied over time: 0.07–0.54 cm cm1 yr1 during the first year, 0.09–0.32 cm cm1 yr1 in the second year, and 0.00–0.29 cm cm1 yr1 in the final period (24–81 months). Similarly, there was temporal variation in the relative growth rates of seedling shoot diameters (RGRd): 0.02–0.79 mm mm1 yr1 in the first year, 0.04–0.16 mm mm1 yr1 in the second year, and 0.05–0.27 mm mm1 yr1 in the final period (24–81 months). Lateral root growth rates were lower in compacted soils than in undisturbed soil during the first two years (0–24 months, Fig. 2). Seedling growth rates during the early planting stage (0–12 and 12–24 months after planting) did not differ significantly among the seven tree species (ANOVA with Bonferroni correction). However, Parashorea macrophylla grew more slowly that the other species during the late period (24–81 months after planting, data not shown). 3.3. Effects of environmental conditions on seedling performances Soil penetration resistance (10–20 cm depth) was positively correlated with seedling mortality during the early planting period (0–12 months) (multiple regression analysis, p < 0.01, standardized regression coefficient = 0.679, Table 2). However, mortalities in the later periods (12–24 and 24–84 months) were not correlated with soil penetration resistance (Table 2). The lateral root growth rate during the first and second years was inhibited by high soil penetration resistance (p < 0.01, standardized regression coefficient = 0.673), but tap root growth was not related to soil hardness (Table 2). Elevated soil moisture was related to the increased seedling RGR of shoot diameter in the first and second years, but soil moisture content was not correlated with the RGR
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(a) Compacted
Soil depth (cm)
0-5
0-5
5-10
5-10
10-15
10-15
15-20
15-20
20-25
20-25
25-30
25-30
30-35
30-35
35-40
35-40
40-45
40-45
45-50
45-50
50-55
50-55
55-60
55-60 0.0
10.0
20.0
30.0
(b) undisturbed
0.0
Soil penetration resistance (J
10.0
20.0
30.0
cm-1)
Fig. 1. Soil penetration resistance at a depth of 0–60 cm between (a) compacted soil and (b) undisturbed soil. Bars indicate standard error.
(a) Compacted soil
of height. Relative light intensity (RLI) was not related to any of the measures of seedling growth and mortality across all time periods. Soil nutrients, such as nitrogen, phosphorus, and potassium contents, were also not correlated with seedling mortalities or growth rates (Table 2). Tap root length was significantly shorter in compacted soil (40.6 cm) than in undisturbed soil 81 months after planting (61.5 cm, Table 3). However, seedling height, shoot diameter, and lateral root length were not significantly different between compacted and undisturbed soils.
(b) Undisturbed soil
4. Discussion 4.1. Soil disturbance 20 years after logging operations had ended 10cm
10cm
Fig. 2. Examples of excavated root systems in (a) compacted soil and (b) undisturbed soil 24 months after planting. The species excavated was Dryobalanops beccarii. Arrows indicate the soil surface.
More than 20 years after logging operations had ceased, logging disturbance still had an effect on surface soil compaction in the dipterocarp stand that we studied. Effects of compaction were large at soil depths of 0–20 cm in the disturbed area we examined,
Table 2 Stepwise multiple regression analysis of the effects of explanatory environmental factors on seedling relative height, shoot diameter, root growth rates, and mortality. [Soil total nitrogen (N), available phosphorus (P), exchangeable potassium (K), relative light intensity (RLI), soil water, and soil penetration resistance at the depth of 0–10 cm and 10–20 cm]. Dependent variable
Lateral root growth rate during 0–24 months (cm year1) Tap root growth rate during 0–24 months (cm year1) RGRh during 0–12 months (cm cm1 year1) RGRh during 12–24 months (cm cm1 year1) RGRh during 24–81 months (cm cm1 year1) RGRd during 0–12 months (mm mm1 year1) RGRd during 12–24 months (mm mm1 year1) RGRd during 24–81 months (mm mm1 year1) Mortality during 0–12 months (%) Mortality during 12–24 months (%) Mortality during 24–81 months (%)
Adjusted R2
Explanatory variables N
P
K
RLI
Soil water
Penetration resistance (0–10 cm)
Penetration resistance (10–20 cm)
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – – – – – – –
– – – – – 0.663** 0.666** – – – –
– – – – – – – – – – –
0.673** – – – – – – – 0.679** – –
0.407 – – – – 0.393 0.396 – 0.416 – –
RGRh, relative growth rate of seedlings height. RGRd, relative growth rate of seedlings diameter. Standardized regression coefficients, significance levels, and adjusted R2 values are given. n = 14. –, Data not selected by the analysis. ** p < 0.01. Unsuitable explanatory variables were excluded by the stepwise procedure (Fin = 0.05 > Fout = 0.1)
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Table 3 Comparison of soil penetration resistance, seedling height, shoot diameter, lateral root length and tap root length, between compacted and undisturbed soil 81 months after planting. Compacted soil
Soil penetration resistance at 0–20 cm (J cm1) Soil penetration resistance at 20–60 cm (J cm1) Height (cm) Diameter (mm) Lateral root length (cm) Tap root length (cm)
Undisturbed soil
Mean
SE
n
Mean
SE
n
6.80 14.52 227.3 21.5 36.0 40.6
0.37 1.00 24.1 1.3 3.2 4.9
19 19 19 19 19 19
3.24 5.21 233.1 22.3 41.3 61.5
0.20 0.38 20.3 1.6 8.7 4.9
16 16 16 16 16 16
** **
ns ns ns **
Values are means and standard errors (SE). ** p < 0.01; analysis of variance (ANOVA). ‘ns’ means not significantly differences.
and soil hardness increased with depth (Fig. 1). We compared levels of surface soil compaction with those in other logged tropical forests using soil bulk density as a measure; this parameter was significantly positively related to soil penetration resistance at our site. Bulk density is usually higher on log landings and skid trails than in undisturbed forest soils (Nussbaum and Ang, 1996). Bulk densities in uncompacted plots at our site (0.98–1.20 g cm3) were within the range of those in other undisturbed dipterocarp forest soils (0.98–1.27 g cm3; Jusoff and Majid, 1986, 1987; Pinard et al., 1996; Van der Plas and Bruijnzeel, 1993). The highest bulk density in our study area was 1.61 g cm3, a value at the upper end of the range reported by other studies of harvesting effects in tropical forests, including log landings and skid trails in logged-over dipterocarp forests (1.00–1.66 g cm3, Nussbaum and Ang, 1996; Nussbaum et al., 1995b; Van der Plas and Bruijnzeel, 1993). Our highest value was comparable to those for forest soils immediately after logging, e.g., 1.49 g cm3 in peninsular Malaysia (Jusoff and Majid, 1987) and 1.44 g cm3 in Sabah, Malaysia (Nussbaum et al., 1995a). The high bulk densities we measured indicated that soil compaction had not recovered naturally over the 20 years since logging had ceased. This protracted period of compaction is consistent with those in other forest biomes, such as temperate forests in which compaction may be elevated more than 40 years after disturbance (Vora, 1988). Although soil compaction was long-lasting, we did not find clear relationships between soil penetration resistance and nutrient contents, e.g., total nitrogen and phosphorus. However, several studies reported decreased nutrient content in soils disturbed by logging, particularly in sites immediately after logging and/or several years after disturbance (Kozlowski, 1999; Nussbaum et al., 1995b). Differences between our study and those at other sites may have resulted from litter accumulation in the Niah Forest Reserve. Leaf litters from regenerated secondary forest trees are usually nutrient-rich (Kenzo et al., 2010). Regenerated trees, such as Macaranga gigantea and M. hosei, reached almost 20 m in height and their crowns covered the disturbed areas, including the skid trail, where we found relatively thick litters in the wheel tracks. There are reports that pioneer species such as Macaranga spp. are able to regenerate on compacted soil and their growth is not retarded except at log landings. In contrast, the establishment and growth of late-successional tree species, especially dipterocarps, are significantly suppressed under compacted soil conditions (Nabe-Nielsen et al., 2007; Nussbaum et al., 1995a; Pinard et al., 2000). In addition, erosion and mineral nutrient loss through surface water runoff after logging disturbance were less severe on the relatively gentle slope in our study plots than in other lowland tropical forests in Sarawak (e.g., Ishizuka et al., 2000). 4.2. Effects of soil compaction on planted seedlings Higher surface soil compaction (at 10–20 cm depth) inhibited lateral root growth and accelerated seedling mortality in the early
stages (0–24 months after planting), but did not affect mortality in the later stages or the seedling shoot growth rate across the whole study period (Table 2). The soil depths (10–20 cm) in which there were effects of compaction on mortality and lateral root elongation may relate to the planting-hole depth (20 cm) we used. During the early planting period, seedlings on compacted soil may have suffered from drought stress caused by limited water absorption by inhibited lateral roots, which were usually not able to grow out of the planting holes, even two years after planting (Fig. 2). Furthermore, increased bulk density usually reduces the water-holding capacity of compacted soil (Chauvel et al., 1991; Jusoff, 1991; Nussbaum et al., 1995a). Thus, drought in the early period after planting likely affected seedling mortality negatively. We found many dead seedlings with wilted leaves in a severely compacted area during a period of approximately two weeks without rain in the initial planting period (three months after planting, T. Kenzo, personal observation). Rubiah and Kamis (2003) examined drought responses of dipterocarp seedlings (Hopea odorata) to soil compaction treatments, demonstrating that high bulk density increases the sensitivity of seedlings to drought stress and leads to a reduction of seedling photosynthesis and stomatal conductance three months after planting in a nursery. Rubiah and Kamis (2003) also reported a reduction in drought sensitivity 12 months after planting due to the elongation of new roots. The increased shoot diameter growth rate under higher soil water conditions in our experiment also highlights the importance of water for seedlings during the early planting stages (Table 2). All of these data for early seedling growth stages were consistent with the reduced effects of soil compaction on mortality and height and diameter growth in the later period, 81 months after planting (Tables 2 and 3). In older seedlings, lateral root elongation did not differ between compacted and undisturbed soil, although tap root elongation was inhibited in the compacted area (Table 2). The tap roots were unable to penetrate beyond more than 40 cm depth in compacted soil, which likely relates to the very hard soils that we detected in the 30–45 cm depth range, where hardness was more than double that of surface soil (Fig. 1). 4.3. Amelioration of soil compaction in enrichment planting Development of an appropriate enrichment planting methodology for dipterocarp seedlings under compacted soil conditions is needed to reduce seedling mortality during the early planting stage and enhance the seedling growth rate in later stages. Nussbaum et al. (1995a) tested the effects of five treatment combinations (compacted soil with fertilizer, compacted soil with mulching, dug soil, dug soil with fertilizer, and replacement of top soil) on the growth of two species of dipterocarp seedlings (Dryobalanops lanceolata and Shorea leprosula), and demonstrated that fertilization was the most effective treatment for improved growth. Vincent and Davies (2003) reported the same fertilization effect for Dryobalanops aromatica and Shorea parvifolia. Many earlier experiments had
D. Hattori et al. / Forest Ecology and Management 310 (2013) 770–776
monitoring periods of only 1–2 years, but longer term observations are required to confirm the effects of fertilizer on dipterocarp seedling growth because negative effects of chemical fertilization, such as decreased growth and spindly morphology probably become apparent after fertilizer treatment has ended (Irino et al., 2004, 2005). Removal of competing non-timber trees also enhances dipterocarp seedling growth after the late planting period (Kuusipalo et al., 1996; Pariona et al., 2003). Future investigations of appropriate procedures for soil compaction amelioration at enrichment planting sites in logged-over dipterocarp forests should be more protracted and extend beyond the seedling stage. 4.4. Conclusions Soil compaction measured by high soil bulk density and penetration resistance was still apparent more than 20 years after a dipterocarp forest had been logged-over. During the early planting period, inhibition of lateral root elongation in the compacted area increased the mortality rates of dipterocarp seedlings. However, soil compaction did not affect the mortality, growth, and lateral root elongation after the late planting period (81 months after planting). Successful enrichment planting of dipterocarp trees in compacted soils requires proper treatment to reduce seedlings mortality in the early planting period. Acknowledgements We thank Sarawak Forest Department and Sarawak Forest Corporation for assistance in our study. This work was partly supported by a Grant-in-Aid for Scientific Research (09NP0901, 13575038, and 17405031), the Nissay Foundation, and the Sasakawa Scientific Research Grant from The Japan Science Society (15-411). References Ådjers, G., Hadengganan, S., Kuusipalo, J., Nuryanto, K., Vesa, L., 1995. Enrichment planting of dipterocarps in logged-over forests: effect of width, direction and maintenance method of planting line on selected Shorea species. For. Ecol. Manage. 73, 271–277. Alameda, D., Villar, R., 2009. Moderate soil compaction; implications on growth and architecture in seedlings of 17 woody plant species. Soil Tillage Res. 103, 325– 331. Alegre, J.C., Cassel, D.K., 1996. Dynamics of soil physical properties under alternative systems to slash-and-burn. Agric. Ecosyst. Environ. 58, 39–48. Appanah, S., Weinland, G., 1996. Experience with planting dipterocarps in peninsular Malaysia. In: Schulte, A., Schöne, D. (Eds.), Dipterocarp Forest Ecosystems: Towards Sustainable Management. World Scientific, Singapore, pp. 411–445. Baillie, I.C., 1972. Report on a Detailed Examination of Soils of Silvicultural Research Plot 53, Niah Forest Reserve, Forest Department Sarawak, Kuching. Black, C.A., 1965. Method of Soil Analysis, Part I. American Society of Agronomy, Madison, Wisconsin. Bray, R.H., Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils. Soil Sci. 59, 39–45. Bruenig, E.F., 1996. Conservation and Management of Tropical Rainforests: An Integrated Approach to Sustainability. CAB International, Wallingford. Cannon, C.H., Peart, D.R., Leighton, M., Kartawinata, K., 1994. The structure of lowland rainforest after selective logging in west Kalimantan, Indonesia. For. Ecol. Manage. 67, 49–68. Chai, D.N.P., 1975. Enrichment planting in Sabah. Malays. For. 38, 271–277. Chauvel, A., Grimaldi, M., Tessier, D., 1991. Changes in soil pore-space distribution following deforestation and revegetation: an example from the Central Amazon Basin, Brazil. For. Ecol. Manage. 38, 259–271. Fredericksen, T.S., Pariona, W., 2002. Effect of skidder disturbance on commercial tree regeneration in logging gaps in a Bolivian tropical forest. For. Ecol. Manage. 171, 223–230. Haile, N.S., 1962. The geology and mineral resources of Suai-Baram Area, North Sarawak. Brit. Borneo Geol. Mem. 13, 176. Hansen, T.S., 2005. Spatio-temporal aspects of land use and land cover changes in the Niah catchment, Sarawak, Malaysia. Singapore J. Trop. Geo. 26, 170–190. Hattori, D., Sabang, J., Tanaka, S., Kendawang, J.J., Ninomiya, I., Sakurai, K., 2005. Soil characteristics under three vegetation types associated with shifting cultivation in a mixed dipterocarp forest in Sarawak, Malaysia. Soil Sci. Plant Nutr. 51, 231– 241.
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